// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_NODE_UTXO_SNAPSHOT_H
#define BITCOIN_NODE_UTXO_SNAPSHOT_H

#include <chainparams.h>
#include <kernel/chainparams.h>
#include <primitives/blockhash.h>
#include <serialize.h>
#include <util/chaintype.h>
#include <util/fs.h>
#include <validation.h>

#include <optional>

// UTXO set snapshot magic bytes
static constexpr std::array<uint8_t, 5> SNAPSHOT_MAGIC_BYTES = {
    {'u', 't', 'x', 'o', 0xff}};

struct BlockHash;

namespace node {
//! Metadata describing a serialized version of a UTXO set from which an
//! assumeutxo Chainstate can be constructed.
//! All metadata fields come from an untrusted file, so must be validated
//! before being used. Thus, new fields should be added only if needed.
class SnapshotMetadata {
    inline static const uint16_t VERSION{2};
    const std::set<uint16_t> m_supported_versions{VERSION};

public:
    //! The hash of the block that reflects the tip of the chain for the
    //! UTXO set contained in this snapshot.
    BlockHash m_base_blockhash;

    //! The number of coins in the UTXO set contained in this snapshot. Used
    //! during snapshot load to estimate progress of UTXO set reconstruction.
    uint64_t m_coins_count = 0;

    SnapshotMetadata() {}
    SnapshotMetadata(const BlockHash &base_blockhash, uint64_t coins_count)
        : m_base_blockhash(base_blockhash), m_coins_count(coins_count) {}

    template <typename Stream> inline void Serialize(Stream &s) const {
        s << SNAPSHOT_MAGIC_BYTES;
        s << VERSION;
        s << Params().DiskMagic();
        s << m_base_blockhash;
        s << m_coins_count;
    }

    template <typename Stream> inline void Unserialize(Stream &s) {
        // Read the snapshot magic bytes
        std::array<uint8_t, SNAPSHOT_MAGIC_BYTES.size()> snapshot_magic;
        s >> snapshot_magic;
        if (snapshot_magic != SNAPSHOT_MAGIC_BYTES) {
            throw std::ios_base::failure(
                "Invalid UTXO set snapshot magic bytes. Please check if this "
                "is indeed a snapshot file or if you are using an outdated "
                "snapshot format.");
        }

        // Read the version
        uint16_t version;
        s >> version;
        if (m_supported_versions.find(version) == m_supported_versions.end()) {
            throw std::ios_base::failure(
                strprintf("Version of snapshot %s does not match any of the "
                          "supported versions.",
                          version));
        }

        // Read the network magic (pchMessageStart)
        CMessageHeader::MessageMagic message;
        s >> message;
        if (!std::equal(message.begin(), message.end(),
                        Params().DiskMagic().data())) {
            auto metadata_network = GetNetworkForMagic(message);
            if (metadata_network) {
                std::string network_string{
                    ChainTypeToString(metadata_network.value())};
                throw std::ios_base::failure(
                    strprintf("The network of the snapshot (%s) does not match "
                              "the network of this node (%s).",
                              network_string, Params().GetChainTypeString()));
            } else {
                throw std::ios_base::failure(
                    "This snapshot has been created for an unrecognized "
                    "network. This could be a new testnet or possibly caused "
                    "by data corruption.");
            }
        }

        s >> m_base_blockhash;
        s >> m_coins_count;
    }
};

//! The file in the snapshot chainstate dir which stores the base blockhash.
//! This is needed to reconstruct snapshot chainstates on init.
//!
//! Because we only allow loading a single snapshot at a time, there will only
//! be one chainstate directory with this filename present within it.
const fs::path SNAPSHOT_BLOCKHASH_FILENAME{"base_blockhash"};

//! Write out the blockhash of the snapshot base block that was used to
//! construct this chainstate. This value is read in during subsequent
//! initializations and used to reconstruct snapshot-based chainstates.
bool WriteSnapshotBaseBlockhash(Chainstate &snapshot_chainstate)
    EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

//! Read the blockhash of the snapshot base block that was used to construct the
//! chainstate.
std::optional<BlockHash> ReadSnapshotBaseBlockhash(const fs::path &chaindir)
    EXCLUSIVE_LOCKS_REQUIRED(::cs_main);

//! Suffix appended to the chainstate (leveldb) dir when created based upon
//! a snapshot.
constexpr std::string_view SNAPSHOT_CHAINSTATE_SUFFIX = "_snapshot";

//! Return a path to the snapshot-based chainstate dir, if one exists.
std::optional<fs::path> FindSnapshotChainstateDir(const fs::path &data_dir);

} // namespace node

#endif // BITCOIN_NODE_UTXO_SNAPSHOT_H
